Renewable switch construction



June 26, 1962 A. J. BlssoNETTE ETAL 3,041,568

RENEWABLE SWITCH CONSTRUCTION Filed Aug. 7, 1959 H .AQUI DH SII.

Irllnlll I IJ l `second mentioned resistive coatings.

vgradually approaching the said header.

United States 3,041,568 RENEWABLE SWITCH CONSTRUCTION Alfred J.Bissonette, Milford, and Robert D. Lapp, Cincinnati, Ohio, assignors toThe Baldwin Piano Company, Cincinnati, Ohio, a corporation of Ohio FiledAng. 7, 1959, Ser. No. 832,317 8 Claims. (Cl. 3238-69) This inventionhas to do with resistive switches such as `are employed to produce agradual onset of the tones in electrical musical instruments when aplaying key is depressed, or putting this another way, switches whichare designed to eliminate undesirable key clicks or surges of current atthe time an, oscillator in continuous operation is connected to` anoutput system.

-A typey of resistive switch which has been very widely used for thepurposes set forth above is that shown in United States Patent No.2,215,124 to Kock and Jordan, issued September 17, 1940.

In the structure of the said United States patent there are formed nearone edge of an insulative base a plurality of-resistive coatingsextending in parallelism toward the opposite edge. On the ,secondopposite edge there is another series of resistive coatings extending inparallelism toward the iirst but interconnected by a common conductor inthe nature of a bus bar or header at the edge of the insulative base.The iirst mentioned resistive coatings are provided with individualconnectors so that each may be electrically coupled to an oscillatorL orgenerator in :a bank of such devices. Attached to the inner ends of thefirst mentioned resistive coatings Ithere are switch blades, one `foreach such coating, and so configured that they normally extend over butout of contact with the vlf one of these switch blades is depressed, asby the engagement olf-a plunger with its outer end it will be broughtagainst the inner end of the appropriate resistive coating of the second'mentioned group. As the switch blade is further depressed it will rockover the second mentioned resistive coating, its point or points ofcontact therewith In some forms of the switch, the switch blades, ifactuated yfar enough, will ultimately contact the header itselfestablishing direct electricalconnection. The iirst mentioned resistivecoatings act as isolating resistors for the several generators. Thesecond mentioned resistive coatings coact with the switch blades to formiirst a high impedance connection between the generator and the bus orheader, which con- 'nection becomes of lower and lower impedance as theswitch blade is further actuated. l

Resistive switches of this character are relatively inex- 'pensive andhave given a good account of themselves in practice. The resistivecoatings as well as the header are usually sprayed on the insulativebase through a template "or mask. The switches are readily formed ingangs of kvarying length containing a considerable number o-f individualswitches; and switch structures of the type described "can readily beused in tandem so that the depression of switch blades themselves arethin and if made of suitable 4rresilient metal,'are not generallysubject to failure.

Where failure occurs it is usually due to a wearinfy or abrasion oftheresistive coatings of thesecond series mentioned above. While it is anadvantage of the switch 3,041,568 Patented June 26, 1962 ICC - which isexpensive and time consuming.

The principal object of this invention is the provision of a switchstructurewhich is capable of being adjusted one or more times in such away that fresh portions of the resistive coatings of the secondmentioned series can be presented to the switch blades. Thus, in thepractice of the invention, a bare adustment of the switching meansbecomes equivalent to a replacement, the adjustment being readilyaccomplished Iin a very short space of time. The above and other objectsof the invention which will be set forth hereinafter or will be apparentto one skilled in the art upon reading these 'specications, areaccomplished by that certain construction and arrangement of pants ofwhich an exemplary embodiment will now be described. Reference is madeto the accompanying drawings where- FIG. 1 is a plan view of a switch4gang embodying the principles of the invention.

FIG. 2 is a cross sectional view thereof taken along the sectionl line2-2 of FIG.v 1 and showing the relationship of the switching mechanismto a playing key. p

FIG. 3 is a plan view from the underside of one section of the switchingmechanism.

- FIG. 4 is a perspective View of -a switch blade. FIG. 5 is a sectionalview -across a portion ofithe same switch blade taken along kthe sectionline S-Sof FIG. 4. Brieiiy, in the practice of the invention a gangswitch is provided with a unitary base or support which may be a sheetof metal. The gang switch will be supported in fthe' instrument by thissheet of metal; and i-t serves further to mount a series of plungers forgenerally verticaly reciprocation, these plungers adapted to beassociated each with a key and at least one switch in the gang.

v The insulative base which has been mentioned above is -divided intotwo parts longitudinally, these parts being Vlelly arranged -and'interspaced resistive coatings which 4provide for the gradual onsetofthe tones as hereinabove set forth. The said second portion is'arranged to be :movable in a longitudinal direction 'wherebyfresh-'portions of the resistive-coatings may be presented tof theVswitch blades in a -way hereinafterfset forth.

Referring now to the appended drawings, there-is shown av simple andcompact form of switch? construction having two decks.

It y'will lbe understood by the vskilled worker in the art thatadditional decks may be incorporated in ythe structure to -the extentthat it is desirable to cause'the actuation of a large number ofresistive switches vby any given key. Theswit'ch comprisesametallic-base yplate l which may be stiitened lby turning up lits edgeportions as at 3' and 4. The plate may 'be of any Alength suitable to'the inclusion of the'desired number of key switches, and hence is shownas broken longitudinally in FIG. l. The vplate 'is adapted `to besupported in 'electrical musical instrument either at'its ends or uponrails 6 and 7' as shownin FIG. 2to"wliich it may beattached by screws 8.

The base plate provides a bearing for a series of verticallyreciprocable plungers 9. This may be accomplished yby drawing the metalof the plate downwardly as at at the positions of the holes throughwhich the plungers extend, or by the insertion of special members in theform of grommets and the like. It is essential that the plungers slideevenly, frictionlessly and noiselessly in the bearings 10; and it iswithin the spirit of the invention to provide sound absorbing washers 11and other means to this end. The upper portion of the plungers isreduced as at 12, unreduced portions forming platform-like abutmentsagainst which the switch blades hereinafter described engage. Theplungers may be made as long as is required for the operation of as manydecks as may be required. The plungers are of insulative plasticmaterial, preferably such a material as a synthetic resin.

As will be appreciated from FIG. l, each switch deck comprises a rearinsulative plate 15. A series of spaced,

parallel resistive coatings are sprayed on this plate. Preferablymetallic connectors 17 are attached to the outer ends of the resistivecoatings 16. This may be done by grommets or rivets 18 as most clearlyshown in FIG. 2. To the inner ends of the resistive coatings 16 theswitch blades are attached as may again be done by grommets or rivets19. A switch blade is shown in perspective in FIG. 4 and in crosssection in FIG. 5. It comprises an attachment portion 20 to bemaintained in electrical contact with the inner ends of the resistivecoatings 16, a relatively long, narrow and resilient neck portion 21,and a relatively wider operating portion 22. The operating portion istreated in dies to form in it one or two longitudinally extending ribs23. These ribs have the multiple function of stitfening the portion 22of the switch blade, of causing the portion 22 to assume permanently alongitudinally arcuate configuration, and of making direct contact withthe resistive coatings on the other portion of the deck as hereinafterdescribed. The outer end of the switch blade will either be providedwith a hole 24 or a forked coniiguration 25 (FIG. 1) so that the switchblade end can be engaged with its own plunger 9.

The deck element is supported in parallelly spaced relationship to theplate 1 by means of metallic sleeve elements 26 through which pass bolts27 having nuts 28 on their upper ends, usually provided with -lockwashers or lock nuts as desired. If the switch has more than one deckthe several deck elements are placed in spaced relationship by means ofadditional collars 29 on the bolts 27.

The other part of the switch deck comprises an insulative member 30.This member, as most clearly shown in FIG. 3, carries sprayed resistivecoatings 31 extending inwardly in spaced parallel relationship from theouter edge of the member 30. The outer ends of these resistive coatingsare interconnected by a bus or header 32 which is conveniently ametallic coating of low resistance, interconnecting the resistivecoatings and provided with a contact means 33 (again held in place as bygrommets or rivets 34), and of such character that a soldered connectionmay readily be made to it.

It will be understood by the skilled worker in the art that the bus orheader 32 of the switch combination serves as a collector foroscillations transmitted thereto by the switch blades in the normalcourse of their operation. The connectors 17 will be wired to theseveral generators of the electrical musical instrument or to a wiringpanel from which such connections may be made; and, as indicated, theresistive coatings 16 serve as anti-robbing resistors permitting aplurality of connections to any one generator. Inasmuch as the formantfilter systems of many electrical musical instruments attenuate thetones unequally in the treble and bass of the instrument, the switchesmay be made up in gangs handling a comparatively small number of keys,say twelve keys forming an octave lin the tempered scale, and theconnectors 33 may 4 be electrically united with a collector headerthrough appropriate resistors to balance the scale.

In FIG. 2 there is shown a key 35 of the electrical musical instrument.This key may be considered as having a playing portion (not shown)extending to the right of the figure, and an intermediate pivot so thatupon actuation of the key the lowered re-ar end of it will move upwardlyin the direction of the arrow. The key may be provided with a leafspring 36 and a controlling screw 37 to regulate its action upon theplunger 9.

When the key 35 is actuated by the player of the musical instrument, itwill move the plunger 9 upwardly, in turn moving the outer ends of theswitch blades upwardly. By reason of the arcuate configurations of theportions 22 of these switch blades they will first contact the innerends of the resistive coatings 31 establishing a high impedanceconnection between a generator and the header 32. As the plunger 9 movesfurther in its upward travel it will rock over the resistive coating 31because of its arcuate shape as hereinabove described, and will finallycome into contact or very nearly into contact with the header 32. Thusthe impedance of the aforesaid connection is lowered; the tone will havea gradual onset; and key clicks will be avoided.

The second portion 30 of any switch deck may be supported substantiallyin the way described for the iirst portion i.e. by means of bolts 38,collars 39 and 40' and nuts 41. But the deck member 30 is provided withholes 42 for the passage of the bolts 38, which holes are considerablyelongated in the direction of the length of the insulative deck member30. Thus the deck member may be supported and fixed in variouslongitudinal positions.

Because of the arcuate shape of the 'switch blade portion 22 and itsrocking action as hereinabove described, there is a certain degree ofwear produced on the resistive coatings 31. In the case of instrumentsWhich are played for many hours day after day this degree of wear mayeventually produce a roughness in the operation of the switch elementsor even prevent -the formation of Van adequate connection between agenerator and the header 32. In the structure of this invention, whensuch a diiiculty is encountered, it is only necessary to loosen the nuts41 and slide the member 30` longitudinally in either direction. Sincethe width of the resistive coatings 31 is substantially greater than thewidth of the contacting portions of the ribs 23, the result will be thepresentation of -a fresh portion of the resistive coating to these ribs.Thus the useful operative life of switches of this character is at leastdoubled and in some instances may be further increased by largeincrements.

The increase in the operative life of the switch mechanisms will dependon various factors, and in partcula-r the relative widths of theresistive coatings 31 and the contacting portions of the switch blades.In a structure in which the switch blades have a pair of ribs .O60 in.apart, by way of example, a lateral shift of .030 in. might not fullydouble the life of the original structure. But a further great advantageof the structure shown and described herein is that the portion 30 ofthe switch structure may be renewed or replaced with no more rewiringthan is involved in the connectionof the contactor 33 to the desiredcollector in the instrument. The switch blades, being made ofberyllium-copper or other suitable spring metal last far longer than thecontacted resistive surfaces. In the structure of this invention, theelement 30 may be wholly replaced without disturbing any of the wiringbetween the generators and the switches.

As has been indicated the number of decks in each gang switch assemblymay be increased as desired within the scope of the instrument. `It isusual to have a plurality of individual switches operated by each key sothat upon the actuation of the key oscillations of different butharmonically related frequencies may be fed simultaneously intodifferent headers or collectors. The skilled worker in the art willunderstand that the headers or collectors will feed a suitable outputcircuit or crcuits (not shown but consisting usually of a preamplifier,an amplifier and a loud speaker) through suitable voicing circuits whichare controlled by stop tabs.

Modications may be made in the invention without departing from thespirit of it. The invention having been described in a certain exemplaryembodiment what is claimed as new and sought to be secured by LettersPatent is:

1. In a resistive switch mechanism a deck comprising a first insulativepanel and a second insulative panel in side by side and substantiallycoplanar relationship, a switch blade attached to said first insulativepanel and extending across said second insulative panel, a relativelynarrow means on said switch blade for making contact with a resistivecoating, a coating of resistive substance upon said second insulativepanel, the width of said coating being substantially greater than thewidth of said contacting means, and means for mounting said rst andsecond insulative panels movable with respect to each other in aldirection Itransverse said switch blade and through a distance at leastequal to the width of said contacting means, whereby said switch bladecan be caused to Contact a fresh portion of said resistive coating.

2. The structure claimed in claim l wherein said relatively narrow meanson said switch blade comprises at least one longitudinal rib forcontacting said resistive coating. Y

3. The structure claimed in claim l wherein said first insulative panelcarries a resistive coating in contact with said switch blade.

4. In a structure for the purpose described a base member, a pluralityof plungers mounted for longitudinal movement through said base member,and a switch deck comprising a first insulative panel and a secondinsulative panel, said rst insulative panel having attached theretoelongated switch blades a portion of which extends across said secondinsulative panel, reistive coatings on said second insulative panel foreach of said switch blades and arranged to be contacted thereby whensaid switch blades are actuated, -means for mounting said irst andsecond insulative panels in spaced relationship to said base and inparallelism to each other, connections between said switch blades andsaid pl'ungers respectively and means for effecting a relative shift inthe longitudinal positions of said first and second insulative panelswhereby to alter the area of contact of said switch blades with saidresistive coatings and connections between said switch blades and saidplungers whereby to cause said switch blades selectively to contact saidresistive coatings.

5. The structure claimed in claim 4 wherein said lirst mentionedinsulative panel carries resistive coatings in contact with said switchblades and means for making contact with said several resistivecoatings.

6. The structure claimed in claim 5 wherein each switch blade comprisesa mounting portion fastened to the first mentioned insulative panel, arelatively narrow resilient neck portion, and a relatively wideroperating end, which operating end is `configured to present at leastone relatively narrow rib to the resistive coatings on said secondinsulative panel and wherein the operating ends of said switch bladeshave a longitudinally arcuate configuration so that they will rock overthe resistive coatings on said second insulative panel.

7. The structure claimed in claim 6 wherein the resistive coatings onsaid second insulative panel have their outer ends interconnected by aconductive coating on said insulative panel.

8. In a resistive switch mechanism, a deck comprising a first insulativepanel and .a second insulative panel, `a switch blade attached to saidrst insulative panel and extending across said second insulative panel,a coating of resistive substance upon said second insulative panel, ameans on said switch blade substantially narrower than said coating formaking contact therewith, and independent means for mounting said -firstand second insulative panels upon a support inV substantially coplanarrelationship, said second insulative panel being movable transversely ofsaid switch blade a distance at least equal to said contacting meanswithout disturbing said Iirst in- -sulative panel and said switch blade.

References Cited in the tile of this patent UNITED STATES PATENTS

